The present invention relates to an imaging lens for forming an image of an object on an imaging element such as a CCD sensor and a CMOS sensor. More particularly, the present invention relates to an imaging lens suitable for mounting in a relatively small camera such as a cellular phone, a digital still camera, a portable information terminal, a security camera, an onboard camera, and a network camera.
An imaging lens to be mounted in a small-sized camera is required to have a lens configuration with high resolution that can be suitably applied to an imaging element of high resolution that is available in these years, in addition to having a small size. Conventionally, there have been various proposals for lens configurations, and among them, an imaging lens with a three-lens configuration has been used in many cameras since it is possible to relatively satisfactorily correct aberrations and easily achieve miniaturization.
For such an imaging lens with the three-lens configuration, for example, an imaging lens described in Patent Reference has been known. The imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; and a third lens having positive refractive power, arranged in the order from an object side. According to the configuration, the third lens has shorter focal length than that of the whole lens system, i.e., the third lens has relatively strong refractive power, and at the same time, the second lens has stronger refractive power than the first lens, so as to correct field curvature, coma aberration, and so on.    Patent Reference: Japanese Patent Application Publication No. 2008-76594
In these years, starting with the cellular phone, there have been rapid advancements in miniaturization and higher resolution of the cameras, and demands for performances of the imaging lenses have been even higher than before. According to the imaging lens described in Patent Reference, although it is possible to relatively satisfactorily correct aberrations, since the whole lens system has a long focal length, the length of the imaging lens on an optical axis is long and there is limitation in miniaturization of the imaging lens.
Here, such a requirement of attaining both miniaturization and aberration correction is not only a challenge specific to the imaging lens for mounting in a cellular phone, but also a challenge for an imaging lens for mounting in a relatively small camera, such as digital still cameras, portable information terminals, security cameras, onboard cameras, and network cameras.
In view of the above-described problems in the conventional techniques, an object of the present invention is to provide an imaging lens that can satisfactorily correct aberrations despite of a small size thereof.
Further objects and advantages of the invention will be apparent from the following description of the invention.